This project is designed to elucidate aspects of the composition and enzymatic activities of isolated adenohypophysial secretory granules which are relevant to the secretion of growth hormone and prolactin. Antibodies will be raised against the high molecular weight disulfide polymers of growth hormone and prolactin found in the granules, and the radioreceptor assay activity of these polymers assessed. Attempts will be made to settle definitively the question of whether or not a non-hormonal intragranular core protein exists. We have recently purified a novel pituitary thioltransferase, and showed it to be capable of utilizing the disulfide polymers as substrates. Its possible role in hormone secretion will be probed directly by immunologic means, utilizing antisera to be generated. Isolated secretory granule membranes, recently shown by us to contain active Mg ions-ATPase and neutral protease activities, will be studied intensively in order to characterize these activities fully, solubilize and purify them, and raise antisera to be used in neutralization experiments to probe the role of the enzymes in secretion. In addition, radioimmunoassays for the enzymes will be developed and, if changes in enzyme activity can be detected in various secretory states, these assays will discriminate between activation/inhibition and changes in enzyme turnover. The component of the granule membrane responsible for our recently demonstrated binding of microtubules to granules and granule membranes will be identified. Factors which may play a role in the puerperal increase in the affinity of the rabbit mammary prolactin receptor for its hormone will be investigated.